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Goodwill and Other Intangible Assets - Schedule of Goodwill and Other Intangible Assets (Details) - USD ($) $ in Millions | Sep. 30, 2018 | Dec. 31, 2017
--- | --- | ---
Goodwill [Line Items] |  |
Goodwill, acquisition date fair value | $ 321.4 | $ 25.9
Goodwill | 321.4 | 25.9
Other intangible assets, accumulated amortization | 47.7 | 34.8
Goodwill and intangible assets, acquisition date fair value | 532.9 | 96.9
Goodwill and intangible assets, net carrying value | 485.2 | 62.1
NSM Holding Co LLC |  |
Goodwill [Line Items] |  |
Goodwill, acquisition date fair value | 295.5 | 0.0
Goodwill | 295.5 | 0.0
Other intangible assets, acquisition date fair value | 140.5 | 0.0
Other intangible assets, accumulated amortization | 5.0 | 0.0
Other intangible assets, net carrying value | 135.5 | 0.0
MediaAlpha |  |
Goodwill [Line Items] |  |
Goodwill, acquisition date fair value | 18.3 | 18.3
Goodwill | 18.3 | 18.3
Other intangible assets, acquisition date fair value | 69.9 | 69.9
Other intangible assets, accumulated amortization | 42.3 | 34.5
Other intangible assets, net carrying value | 27.6 | 35.4
Buzzmove |  |
Goodwill [Line Items] |  |
Goodwill, acquisition date fair value | 7.6 | 7.6
Goodwill | 7.6 | 7.6
Other intangible assets, acquisition date fair value | 1.1 | 1.1
Other intangible assets, accumulated amortization | 0.4 | 0.3
Other intangible assets, net carrying value | 0.7 | 0.8
Customer relationships | NSM Holding Co LLC |  |
Goodwill [Line Items] |  |
Other intangible assets, acquisition date fair value | 85.5 | 0.0
Other intangible assets, accumulated amortization | 3.6 | 0.0
Other intangible assets, net carrying value | 81.9 | 0.0
Customer relationships | MediaAlpha |  |
Goodwill [Line Items] |  |
Other intangible assets, acquisition date fair value | 26.8 | 26.8
Other intangible assets, accumulated amortization | 4.3 | 2.4
Other intangible assets, net carrying value | 22.5 | 24.4
Trade names | NSM Holding Co LLC |  |
Goodwill [Line Items] |  |
Other intangible assets, acquisition date fair value | 51.2 | 0.0
Other intangible assets, accumulated amortization | 1.1 | 0.0
Other intangible assets, net carrying value | 50.1 | 0.0
Trade names | Buzzmove |  |
Goodwill [Line Items] |  |
Other intangible assets, acquisition date fair value | 0.6 | 0.6
Other intangible assets, accumulated amortization | 0.1 | 0.1
Other intangible assets, net carrying value | 0.5 | 0.5
Information technology | NSM Holding Co LLC |  |
Goodwill [Line Items] |  |
Other intangible assets, acquisition date fair value | 3.8 | 0.0
Other intangible assets, accumulated amortization | 0.3 | 0.0
Other intangible assets, net carrying value | 3.5 | 0.0
Information technology | MediaAlpha |  |
Goodwill [Line Items] |  |
Other intangible assets, acquisition date fair value | 33.3 | 33.3
Other intangible assets, accumulated amortization | 29.2 | 24.3
Other intangible assets, net carrying value | 4.1 | 9.0
Information technology | Buzzmove |  |
Goodwill [Line Items] |  |
Other intangible assets, acquisition date fair value | 0.5 | 0.5
Other intangible assets, accumulated amortization | 0.3 | 0.2
Other intangible assets, net carrying value | 0.2 | 0.3
Other | MediaAlpha |  |
Goodwill [Line Items] |  |
Other intangible assets, acquisition date fair value | 9.8 | 9.8
Other intangible assets, accumulated amortization | 8.8 | 7.8
Other intangible assets, net carrying value | 1.0 | 2.0
Other Intangible Assets |  |
Goodwill [Line Items] |  |
Other intangible assets, acquisition date fair value | 211.5 | 71.0
Other intangible assets, accumulated amortization | 47.7 | 34.8
Other intangible assets, net carrying value | 163.8 | 36.2
Non-controlling interest |  |
Goodwill [Line Items] |  |
Goodwill and intangible assets, net carrying value | (40.6) | (21.1)
Total |  |
Goodwill [Line Items] |  |
Goodwill and intangible assets, net carrying value | $ 444.6 | $ 41.0

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